1. Field of the Invention
The present invention relates to energy transfer methods and apparatus. More particularly, the invention relates to providing a sufficiently stable power to a load in an energy transfer system that transfers power across a physical boundary (e.g., from a power supply located external to a body to a load located internal to the body).
2. Related Art
In a variety of scientific, industrial, and medically related applications, it may be desirable to transfer energy or power (energy per unit time) across some type of boundary. For example, one or more devices that require power (e.g., electrical, mechanical, optical, and acoustic devices) may be located within the confines of a closed system, or xe2x80x9cbody,xe2x80x9d in which it may be difficult and/or undesirable to also include a substantial and/or long term source of power. The closed system or body may be delimited by various types of physical boundaries, and the system internal to the boundary may be living or inanimate, may perform a variety of functions, and may have a variety of operational and physical requirements and/or constraints. In some cases, such requirements and constraints may make the implementation of a substantial and/or long term xe2x80x9cinternalxe2x80x9d power source for internally located devices problematic.
In some closed systems, repeated entry into the system may be undesirable for a variety of reasons. In other closed systems, significant internal power requirements and a limited internal space may prohibit the implementation of a suitably sized internal power source. In yet other systems, contamination and/or security issues may pose particular challenges in implementing an internal power source For any combination of the foregoing and other reasons, a power source external to the system and some feasible means of transferring power from the external source to one or more internal devices may be preferable in some applications.
One example of a closed system is the human body. In some medically related and scientific applications, a variety of prosthetic and other devices that require power may be surgically implanted within various portions of the body. Some examples of such devices include a synthetic replacement heart, a circulatory blood pump or ventricular assist device (VAD), a cochlear (ear) implant, a pacemaker, and the like. With respect to the human body, issues such as repeated reentry or surgery, internal space limitations, and contamination (e.g., infection) may make the implementation of a suitable internal power source for some of these implanted devices impractical.
Accordingly, in some medical implant applications, xe2x80x9ctranscutaneous energy transferxe2x80x9d (TET) devices are employed to transfer energy from outside the body to inside the body, to provide power to one or more implanted prostheses or devices from an external power source. One example of a conventional TET device is a transformer that includes a primary winding (or coil) external to the body and a secondary winding internal to the body. Both the primary and secondary windings generally are placed proximate to respective outer and inner layers of a patient""s skin; hence, the term xe2x80x9ctranscutaneousxe2x80x9d commonly refers to energy transfer xe2x80x9cthrough the skin.xe2x80x9d Energy is transferred from the primary winding to the secondary winding in the form of a magnetic field. The implanted secondary winding converts the transferred energy in the magnetic field to electrical power for the implanted device, which acts as a xe2x80x9cloadxe2x80x9d on the secondary winding.
In general, TET devices differ from conventional power transformers in that power transformers typically include a magnetic core around which the primary and secondary windings are wound, thus fixing the relative positions of the primary and secondary windings. In contrast, the primary and secondary windings of conventional TET devices are not necessarily fixed in position with respect to one another. Accordingly, one issue associated with conventional TET devices is that the power supplied by the secondary winding to a load (e.g., an implanted device) may be quite sensitive to more than nominal or trivial physical displacements of either the primary winding or the secondary winding from an optimum coupling position. The resolution of this issue determines the suitability of the TET technology to a particular type of load.
For example, implanted prostheses or other devices, and particularly an implanted device that performs a life sustaining function, generally must have a consistent source of available power. Without a consistent power source, the implanted device may function erratically or intermittently. Such an erratic or intermittent operation can have undesirable, and in some cases serious life threatening effects on the patient. Accordingly, with TET devices in particular, and other energy transfer systems in general which transfer energy across a boundary, it is desirable to accurately and reliably provide a sufficiently stable power to the load.
One embodiment of the invention is directed to an apparatus for use in a transcutaneous energy transfer system that includes a power supply, a primary winding and a secondary winding. The apparatus comprises a control circuit, coupled to the power supply and the primary winding, to monitor a primary amplitude of a primary voltage across the primary winding and to control the primary amplitude based only on the monitored primary amplitude and a reference voltage.
Another embodiment of the invention is directed to a method in a transcutaneous energy transfer system including a power supply, a primary winding and a secondary winding. The method comprises acts of monitoring a primary amplitude of a primary voltage across the primary winding, and regulating the primary amplitude based only on the monitored primary amplitude and a reference voltage.
Another embodiment of the invention is directed to an energy transfer system for transferring power from a power supply located on a first side of a physical boundary to a variable load located on a second side of the physical boundary. The energy transfer system comprises a primary winding electrically coupled to the power supply to generate a magnetic field based on input power provided by the power supply, wherein the magnetic field permeates the physical boundary. The system also comprises a secondary winding, magnetically coupled to the primary winding via the magnetic field, to receive at least a portion of the magnetic field. The secondary winding is electrically coupled to the variable load to provide output power to the variable load based on the received magnetic field. The system also comprises at least one control circuit, electrically coupled to at least the primary winding, to regulate a primary voltage across the primary winding such that a sufficiently stable output power is provided to the variable load notwithstanding at least one of changes in the load and changes in a relative position of the primary winding and the secondary winding.
Another embodiment of the invention is directed to a method of transferring power from a power supply to a variable load in an energy transfer system that includes a primary winding electrically coupled to the power supply located on a first side of a physical boundary, and a secondary winding electrically coupled to the variable load located on a second side of the physical boundary. The method comprises an act of regulating a primary voltage across the primary winding so as to provide a sufficiently stable output power to the variable load notwithstanding at least one of changes in the variable load and changes in a relative position of the primary winding and the secondary winding.
Another embodiment of the invention is directed to an apparatus for use in an energy transfer system, wherein the energy transfer system includes a power supply electrically coupled to a primary winding, and a secondary winding magnetically coupled to the primary winding. The primary and secondary windings are used to transfer power from the power supply to a load that is electrically coupled to the secondary winding. The primary winding and the secondary winding do not have a fixed spatial relationship to each other. The apparatus comprises a secondary circuit, electrically coupled to the secondary winding, to monitor a measurable quantity associated with the load and to provide a detectable indication based on the monitored measurable quantity. The apparatus also comprises a primary circuit, electrically coupled to the primary winding, to monitor the detectable indication provided by the secondary circuit and to regulate a primary voltage across the primary winding based on the detectable indication so as to regulate a load voltage across the load.
Another embodiment of the invention is directed to a method in a transcutaneous energy transfer system that includes a power supply electrically coupled to a primary winding and a secondary winding magnetically coupled to the primary winding. The primary and secondary windings are for transferring power from the power supply to a load that is electrically coupled to the secondary winding. The primary winding and the secondary winding do not have a fixed spatial relationship to each other. The method comprises acts of making a comparison of a measurable quantity associated with the load and a predetermined threshold level, activating a secondary circuit to provide a detectable indication based on the comparison, and regulating a primary voltage across the primary winding based on the detectable indication.
Another embodiment of the invention is directed to an energy transfer system for transferring power from a power supply located on a first side of a physical boundary to a variable load located on a second side of the physical boundary. The energy transfer system comprises a primary winding electrically coupled to the power supply to generate a magnetic field based on input power provided by the power supply, and a secondary winding magnetically coupled to the primary winding to receive at least a portion of the magnetic field generated by the primary winding. The secondary winding provides output power to the variable load based on the received magnetic field, and the magnetic field forms a portion of a power channel between the primary winding and the secondary winding to transfer at least some of the power from the power supply to the variable load. The energy transfer system also comprises a first control circuit, electrically coupled to the primary winding, to regulate a load voltage across the variable load based on information related to the variable load that is obtained via the power channel.
Another embodiment of the invention is directed to a method in an energy transfer system for transferring power from a power supply located on a first side of a physical boundary to a variable load located on a second side of the physical boundary. The energy transfer system includes a primary winding electrically coupled to the power supply to generate a magnetic field based on input power provided by the power supply, and a secondary winding magnetically coupled to the primary winding to receive at least a portion of the magnetic field generated by the primary winding. The secondary winding provides output power to the variable load based on the received magnetic field, and the magnetic field forms a portion of a power channel between the primary winding and the secondary winding to transfer at least some of the power from the power supply to the variable load. The method comprises acts of monitoring the power channel to obtain information related to the variable load, and regulating a load voltage across the variable load based on the information obtained via the power channel.